Many weighing systems are known, some dating back to biblical times. More recently, weighing systems have been developed for weighing each one of a stream of articles, such as mail pieces or parcels moving through a transport or mail sorting system. Prior art systems of that type are shown, for example, in U.S. Pat. Nos. 7,096,152 and 3,648,839.
Some known systems rely on back-EMF or “Electro Magnetic Force Restoration” principles. According to one vendor, “an applied load is compensated for by an electromagnetically produced counterforce. A precision position control (optical) keeps the system stable. The slightest movement is detected, initiates a feedback circuit to run current through a coil and causes the load to be returned to its original position. The coil current, which is proportional to the weight, is transmitted to an internal ND converter then processed in the microprocessor.”
Commonly-owned U.S. Pat. No. 7,687,727 discloses an improved in-line scale for very fast, accurate measurement of moving items such as mailpieces moving along a transport system. However, inaccuracies in such measurements can result from variations in the thickness of the items under measurement. The need remains for improvements in in-line weighing systems.